Inflatable mattresses for air beds and water beds are known. U.S. Pat. Nos. 4,908,895 and 4,991,244 to Walker, and assigned to the assignee of the present application, for instance, disclose sophisticated inflatable mattresses suitable for use in high quality air beds.
The '244 patent to Walker discloses an air mattress M (See FIG. 2) that includes a bladder B and a border support wall W that supports and contains the bladder. The border wall provides shape to the mattress, and limits the outward movement of the bladder. Limiting the outward movement of the bladder in turn limits the degree to which the upper surface of the bladder, supported by fluid within the bladder, can be displaced, providing a degree of firmness to the mattress.
Border walls for mattresses are often made of single density foam approximately 4".times.6" in cross-section. A drawback associated with this type of mattress construction centers around density and inverse load deflection (ILD) rating specifications of the foam. The foam must be firm enough for the border wall to contain the bladder. Foam that is firm enough to provide containment, however, presents an abrupt change in the softness of the bed, making it uncomfortable to sleep near the side of the bed and providing a feeling of "hard edges" under the legs while sitting on the edge of the mattress.
Additionally, solid foam side walls do not allow for air circulation from within the interior of the mattress. Poor air exchange from within the mattress can cause moisture to become entrapped within the mattress, thereby providing a more favorable environment for the growth and development of fungi, bacteria and other microorganisms. As a result, annoying and unpleasant odors can develop and disease causing pathogens can be harbored.
The '244 Walker patent addresses the above described problems by disclosing a double density foam block wall. Again referring to FIG. 2, the double density block wall W includes a higher density lower layer W.sub.I attached to a lower density upper layer W.sub.u to provide a softer sitting edge at the top of the border, and a bladder containment structure below. Although more comfortable than the single density foam border, the method of manufacture, which requires the joining of the two layers, requires additional steps for joining the layers, and the resultant foam block wall does not allow for air exchange. Accordingly, mattresses with foam borders of double density foam, while imparting greater comfort, tend to be more expensive to manufacture and are susceptible to the moisture accumulation problem discussed above.